1. Field
Example embodiments of the present application generally relate to a rotation device to control a rotation driving source such as motors, and to a rotation controlling method, a computer readable medium including a rotation controlling program and an image forming apparatus including the rotation device.
2. Description of the Related Art
Recently, rotation devices for rotating a rotation member, which have a motor and a transmission mechanism to transmit rotation of the motor to the rotation member, are used to various fields, and are demanded to increase accuracy thereof. For example, image forming apparatuses such as printers, copiers, facsimile, etc. employing an electrophotographic method to form a toner image writes an electrostatic latent image on a photoconductor drum by controlling a laser diode (LD) based on image data to form a laser beam and scanning the photoconductor drum with the laser beam in a main-scanning direction while moving the photoconductor drum in a sub-scanning direction. In this regards, the image forming apparatus performs sub-scanning by. rotating the photoconductor drum. When the rotation speed of the photoconductor drum (i.e., sub-scanning speed) fluctuates, the positions of the main-scanning lines vary, resulting in deterioration of image quality.
Particularly, in a color image forming process, a full color image is formed by performing the laser beam scanning four times to form the four color images. Therefore, the sub-scanning speed needs to remain constant to reduce color misalignment. Thus, when the sub-scanning speed fluctuates, image quality deteriorates. Therefore, in order to accurately maintain the rotation speed of a photoconductor drum at a constant level, it is important to control the motor driving the photoconductor drum.
In a related art driving control technique, the rotation angular displacement or rotation angular speed of a rotation axis of a motor driving a photoconductor drum are detected and the rotation of the motor is controlled based on the detection result.
Such driving control reduces rotation speed fluctuation of the motor, thereby rotating the motor at a constant speed. In this way, the driving control may reduce an occurrence of image misalignment and image quality deterioration such as color deviation caused by rotation speed fluctuation of the photoconductor drum resulting from the rotation speed fluctuation of the motor. However, even when the motor rotates at a constant speed, the photoconductor causes the rotation speed fluctuation resulting from eccentricity of each rotation axis.
One example attempts to reduce an influence of the rotation speed fluctuation on a photoconductor drum in a tandem image forming apparatus having four photoconductor drums for four colors. This tandem image forming apparatus forms registration patterns for four colors on an intermediate transfer belt serving as an intermediate transfer member on which the toner image is transferred, and detects the registration patterns by using a sensor. The tandem image forming apparatus determines an eccentric phase component including eccentricity of each photoconductor drum and eccentricity of members such as gears for transmitting to driving force of the driving motor to the photoconductor drum. Therefore, the tandem image forming apparatus controls the motor based on the determined eccentricity and eccentric phase component to decrease phase lag, thereby reducing an occurrence of color misalignment.
Another example attempts to detect the rotation speed fluctuation of a photoconductor drum in image forming apparatus without using an encoder to control a motor based on the detection result such that the photoconductor is not fluctuated. When the image forming apparatus controls the rotation speed of the motor to be a certain level, the image forming apparatus detects a time interval T1 of pulses generated after every half-turn of the photoconductor drum. Then, the image forming apparatus controls the motor by using a measurement sine-wave reference signal that is fluctuated by a rotation cycle of the photoconductor drum, and detects a time interval T2 of pulses generated after every half-turn of the photoconductor drum. The image forming apparatus determines the amplitude and phase of the rotation speed fluctuation of one rotation cycle of the photoconductor drum (i.e., speed fluctuation caused by the eccentricity of the photoconductor drum axis) based on the detection results of T1 and T2. The image forming apparatus controls the motor such that the speed fluctuation of the photoconductor drum is reduced, and the photoconductor drum rotates at a speed.